The present patent application is related to light emitting devices.
Solid-state light sources, such as light emitting diodes (LEDs) and laser diodes, can offer significant advantages over other forms of lighting, such as incandescent or fluorescent lighting. For example, when LEDs or laser diodes are placed in arrays of red, green and blue elements, they can act as a source for white light or as a multi-colored display. In such configurations, solid-state light sources are generally more efficient and produce less heat than traditional incandescent or fluorescent lights. Although solid-state lighting offers certain advantages, conventional semiconductor structures and devices used for solid-state lighting are relatively expensive. One of the costs related to conventional solid-state light emitting devices is related to the relatively low manufacturing throughput of the conventional solid-state light emitting devices.
Referring to FIG. 1, a conventional LED structure 100 includes a substrate 105, which may, for example, be formed of sapphire, silicon carbide, or spinel. A buffer layer 110 is formed on the substrate 105. The buffer layer 110 serves primarily as a wetting layer, to promote smooth, uniform coverage of the sapphire substrate. The buffer layer 110 is typically formed of GaN, InGaN, AlN, or AlGaN and has a thickness of about 100-500 Angstroms. The buffer layer 310 is typically deposited as a thin amorphous layer using Metal Organic Chemical Vapor Deposition (MOCVD).
A p-doped Group III-V compound layer 120 is formed on the buffer layer 110. The p-doped Group III-V compound layer 120 is typically made of GaN. An InGaN quantum-well layer 130 is formed on the p-doped Group III-V compound layer 120. An active Group III-V compound layer 140 is then formed on the InGaN quantum-well layer 130. An n-doped Group III-V compound layer 150 is formed on the layer 140. The p-doped Group III-V compound layer 120 is n-type doped. A p-electrode 160 is formed on the n-doped Group III-V compound layer 150. An n-electrode 170 is formed on the first Group III-V compound layer 120.
A drawback of the conventional LED structure 100 is the low manufacturing throughput associated with the small substrate dimensions. For example, sapphire or silicon carbide substrates are typically supplied in diameters of 2 to 4 inches. Another drawback of the conventional LED structure 100 is that its layered structure often suffers from cracking. Suitable substrates such as sapphire or silicon carbide are typically not available in single crystalline forms. The p-doped Group III-V compound layer 120 can suffer from cracking or delamination due to differential thermal expansions and lattice mismatching between the p-doped Group III-V compound layer and the substrate even in the presence of the buffer layer 110. The differential thermal expansions and lattice mismatching can also produce a bowing deformation (i.e., curling up) in the LED structure. As a result, light emitting performance of the LED structure 100 can be compromised.
Accordingly, there is therefore a need for a light emitting device that can overcome some or all of the drawbacks in the conventional light emitting systems.